Filters

GSAOI contains two filter wheels and one utility wheel. The two filter wheels have room for 27 broad- and narrow-band (zero redshifted) emission- and absorption line- filters. Each filter wheels also contains one blocked position for recording bias and dark frames. The list of the installed filters, central wavelengths, 50% cut-on and cut-off wavelengths, the Gemini Filter Number, transmission curves (plot and ASCII files), and the filter ID (internal) are listed in the table below.

The utility wheel contains a pupil viewer and two defocus lenses (convex and concave). The pupil viewer is used to accurately align the cold stop with GeMS exit pupil viewer and so minimize the background reaching the imager detector. The convex and concave defocus lenses produce defocused images that are used to derive static wave front phase errors at the imager detector. These phase errors are nulled using the GeMS deformable mirrors.

Transmission curves for the filters currently installed in GSAOI are shown in the figure below. The atmospheric transmission between 0.9 and 2.5 μm is superimposed as a dark green line.

The table lists the properties of the filters based on lab measurements. The measurements were taken at room temperature and then calculated to 70 K using correlation measurements from a cold test witness. The measured witnesses were obtained at 298 K and 77 K and the slopes were used to determine the 70 K shift. To access the graph or the ASCII data, click on the links in the table below (plot or data). Note that the filter name is the concatenation of filter and the Gemini filter Number e.g. Z_G1101 for Z broad-band filter and CH4short_G1109 for CH4(short) narrow-band filter.